<template>
  <div class="gj-loadmore">
    <div class="gj-loadmore-content" :class="{ 'is-dropped': topDropped }" :style="{ 'transform': 'translate3d(0, ' + translate + 'px, 0)' }">
      <slot name="top">
        <div class="gj-loadmore-top" v-if="topMethod">
          <div v-show="topStatus === 'loading'"><img src="../assets/images/loading.gif" style="width:40px;height:40px;"/></div>
          <div v-show="topStatus === 'pull'||topStatus === 'drop'"><img src="../assets/images/portfolio/niutou@2x.png" style="width:40px;height:40px;"/></div>
          <div class="w-loadmore-text">{{ topText }}</div>
        </div>
      </slot>
      <slot></slot>
      <slot name="bottom">
        <div class="gj-loadmore-bottom" v-if="bottomMethod">
          <div v-show="bottomStatus === 'loading'"><img src="../assets/images/loading.gif" style="width:40px;height:40px;"/></div>
          <div v-show="bottomStatus === 'pull'||bottomStatus === 'done'"><img src="../assets/images/portfolio/niutou@2x.png" style="width:40px;height:40px;"/></div>
          <span class="w-loadmore-text">{{ bottomText }}</span>
        </div>
      </slot>
    </div>
  </div>
</template>

<style>
.gj-loadmore {
  overflow: hidden;
}

.gj-loadmore-content.is-dropped {
      -webkit-transition: .2s;
      transition: .2s;
  }

.gj-loadmore-top{
  text-align: center;
  height: 60px;
  /*line-height: 50px;*/
}
.gj-loadmore-bottom{
  text-align: center;
  margin-top: 10px;
}

.gj-loadmore-top {
  margin-top: -60px;
}

.gj-loadmore-bottom {
  /*margin-bottom: -60px;*/
}

.gj-loadmore-text {
  vertical-align: middle;
}

.w-loadmore-text{
  color:#999999
}
</style>

<script type="text/babel">
  export default {
    name: 'gj-loadmore',
    props: {
      maxDistance: {
        type: Number,
        default: 0
      },
      autoFill: {
        type: Boolean,
        default: true
      },
      distanceIndex: {
        type: Number,
        default: 2
      },
      topPullText: {
        type: String,
        default: '下拉刷新'
      },
      topDropText: {
        type: String,
        default: '释放更新'
      },
      topLoadingText: {
        type: String,
        default: '加载中...'
      },
      topDistance: {
        type: Number,
        default: 80
      },
      topMethod: {
        type: Function
      },
      bottomPullText: {
        type: String,
        default: '上拉加载更多'
      },
      bottomLoadingText: {
        type: String,
        default: '加载中...'
      },
      bottomAllLoadedText:{
        type: String,
        default: '已全部加载'
      },
      bottomDistance: {
        type: Number,
        default: 80
      },
      bottomMethod: {
        type: Function
      },
      allowLoad: {
        type: Boolean,
        default: true
      }
    },

    data() {
      return {
        translate: 0,
        scrollEventTarget: null,
        containerFilled: false,
        topText: '',
        topDropped: false,
        bottomText: '',
        // bottomReached: false,
        direction: '',
        startY: 0,
        startScrollTop: 0,
        currentY: 0,
        topStatus: '',
        bottomStatus: '',
        bottomAllLoaded:false,
        marginBottom:'60px',
        judge:'block'
      };
    },

    watch: {
      topStatus(val) {
        this.$emit('top-status-change', val);
        switch (val) {
          case 'pull':
            this.topText = this.topPullText;
            break;
          case 'drop':
            this.topText = this.topDropText;
            break;
          case 'loading':
            this.topText = this.topLoadingText;
            break;
        }
      },
      bottomStatus(val) {
        this.$emit('bottom-status-change', val);

        switch (val) {
          case 'pull':
            this.bottomText = this.bottomPullText;
            break;
          case 'done':
            this.bottomText = this.bottomAllLoadedText;
            break;
          case 'loading':
            this.bottomText = this.bottomLoadingText;
            break;
        }
      }
    },

    methods: {
      onTopLoaded() {
        this.translate = 0;
        setTimeout(() => {
          this.topStatus = 'pull';
        }, 200);
      },

      onBottomLoaded() {
        this.bottomStatus = 'pull';

        if (!this.bottomAllLoaded && !this.containerFilled) {
          this.fillContainer();
        }
      },

      onBottomAllLoaded(){
        this.bottomStatus = 'done';
        this.bottomAllLoaded = true;
        this.bottomText = this.bottomAllLoadedText;
      },

      onBottomError(text){ // 错误或数据为空时可调此方法用来隐藏底部牛头
        this.bottomStatus = 'error';
        this.bottomAllLoaded = true;
        this.bottomText = text || '';
      },

      reset(){
        this.$nextTick(() => {
          this.bottomAllLoaded = false;
          this.init();
        });
      },

      getScrollEventTarget(element) {
        let currentNode = element;
        while (currentNode && currentNode.tagName !== 'HTML' &&
          currentNode.tagName !== 'BODY' && currentNode.nodeType === 1) {
          let overflowY = document.defaultView.getComputedStyle(currentNode).overflowY;
          if (overflowY === 'scroll' || overflowY === 'auto') {
            return currentNode;
          }
          currentNode = currentNode.parentNode;
        }
        return window;
      },

      getScrollTop(element) {
        if (element === window) {
          return Math.max(window.pageYOffset || 0, document.documentElement.scrollTop);
        } else {
          return element.scrollTop;
        }
      },

      bindTouchEvents() {
        var vm = this;

        this.scrollEventTarget.addEventListener('touchstart', this.handleTouchStart);
        this.scrollEventTarget.addEventListener('touchmove', this.handleTouchMove);
        this.scrollEventTarget.addEventListener('touchend', this.handleTouchEnd);
        this.scrollEventTarget.addEventListener('scroll', this.handleScroll);
      },

      init() {
        this.topStatus = 'pull';
        this.bottomStatus = 'pull';
        this.topText = this.topPullText;
        this.scrollEventTarget = this.getScrollEventTarget(this.$el);

        if (typeof this.bottomMethod === 'function') {
          this.fillContainer();
          this.bindTouchEvents();
        }
        if (typeof this.topMethod === 'function') {
          this.bindTouchEvents();
        }
      },

      fillContainer() {
        // alert(this.autoFill)
        if (this.autoFill) {
          this.$nextTick(() => {
            if (this.scrollEventTarget === window) {
              this.containerFilled = this.$el.getBoundingClientRect().bottom-50 >=
                document.documentElement.getBoundingClientRect().bottom;
            } else {
              this.containerFilled = this.$el.getBoundingClientRect().bottom-50 >=
                this.scrollEventTarget.getBoundingClientRect().bottom;
            }
            if (!this.containerFilled) {
              this.bottomStatus = 'loading';
              // alert('bottomMethod')
              this.bottomMethod();
            }
          });
        }
      },

      checkBottomReached() {
        if (this.scrollEventTarget === window) {
          return document.body.scrollTop + document.documentElement.clientHeight >= document.body.scrollHeight;
        } else {
          return this.$el.getBoundingClientRect().bottom <= this.scrollEventTarget.getBoundingClientRect().bottom + 1;
        }
      },

      handleTouchStart(event) {
        this.startY = event.touches[0].clientY;
        this.startScrollTop = this.getScrollTop(this.scrollEventTarget);

        if (this.topStatus !== 'loading') {
          this.topStatus = 'pull';
          this.topDropped = false;
        }
      },

      handleTouchMove(event) {
        if (this.startY < this.$el.getBoundingClientRect().top && this.startY > this.$el.getBoundingClientRect().bottom) {
          return;
        }

        this.currentY = event.touches[0].clientY;
        let distance = (this.currentY - this.startY) / this.distanceIndex;
        this.direction = distance > 0 ? 'down' : 'up';
        if (typeof this.topMethod === 'function' && this.direction === 'down' &&
          this.getScrollTop(this.scrollEventTarget) === 0 && this.topStatus !== 'loading') {
          event.preventDefault();
          event.stopPropagation();
          if (this.maxDistance > 0) {
            this.translate = distance <= this.maxDistance ? distance - this.startScrollTop : this.translate;
          } else {
            this.translate = distance - this.startScrollTop;
          }
          if (this.translate < 0) {
            this.translate = 0;
          }
          this.topStatus = this.translate >= this.topDistance ? 'drop' : 'pull';
          this.$emit('translate-change', this.translate);
        }
      },

      handleTouchEnd() {
        if (this.direction === 'down' && this.getScrollTop(this.scrollEventTarget) === 0 && this.translate > 0) {
          this.topDropped = true;
          if (this.topStatus === 'drop') {
            this.translate = '60';
            this.topStatus = 'loading';
            this.topMethod();
          } else {
            this.translate = '0';
            this.topStatus = 'pull';
          }
        }
        this.$emit('translate-change', this.translate);
        this.direction = '';
      },

      handleScroll(event){
        var vm = this;
        if(!vm.allowLoad) return;

        this.$nextTick(function(){
          var bottomReached = vm.checkBottomReached();
          if(typeof this.bottomMethod === 'function' && this.bottomStatus !== 'loading' && !this.bottomAllLoaded && bottomReached) {
            event.preventDefault();
            event.stopPropagation();

            this.bottomStatus = 'loading';
            // alert('bottomMethod')
            this.bottomMethod();
          }
        })
      }
    },

    mounted() {
      this.init();
    },

    beforeDestroy () {
      this.scrollEventTarget.removeEventListener('touchstart', this.handleTouchStart);
      this.scrollEventTarget.removeEventListener('touchmove', this.handleTouchMove);
      this.scrollEventTarget.removeEventListener('touchend', this.handleTouchEnd);
      this.scrollEventTarget.removeEventListener('scroll', this.handleScroll);
    }
  };
</script>
